/Engine/Source/Runtime/UMG/Public/Slate/UMGDragDropOp.h
This is the drag/drop class used for UMG, all UMG drag drop operations utilize this operation. It supports moving aUObjectpayload and using aUWidgetdecorator.
class FUMGDragDropOp : public [FGameDragDropOperation](API\Runtime\SlateCore\Input\FGameDragDropOperation), public [FGCObject](API\Runtime\CoreUObject\UObject\FGCObject)